Current mobile technology trends integrate multiple radio access technologies (RATs) into a single wireless transmit/receive unit (WTRU) that transmits and receives via respective individual antennas, or via a common antenna that is shared through a duplexer filter. Particular specifications for RAT air interfaces are derived based on typical deployment scenarios. In the case of multiple RATs integrated into the same WTRU, self-interference can be significant, which results in receiver desensitization.
FIG. 1 shows an example of a problem that occurs in a conventional transceiver 100 including a transmitter 105, a power amplifier (PA) 110 and a modulator/demodulator (modem) 140, whereby noise generated by the transmitter 105 and the PA 110 causes the modem 140 to jam. The transceiver 100 may also include a duplexer 115, an antenna 120, a low noise amplifier (LNA) 125, a receiver 130 and an analog-to-digital converter (ADC) 135. The duplexer 115 may include a transmit filter 115A and a receive filter 115B. The transmitter 105 outputs a signal that is amplified by the PA 110 and is routed to the antenna 120 via the transmit filter 115A of the duplexer 115. Signals received by the antenna 120 are routed to the modem 140 via the receive filter 115B of the duplexer 115, the LNA 125, the receiver 130 and the ADC 135. The LNA 125 amplifies the received signals, the receiver down-converts the received signals to baseband signals, and the ADC 135 converts the baseband signals to digital signals that are input to the modem 140.
In the example shown in FIG. 1, the output noise density of the PA 115 is −120 dBm/Hz (@+24 dBm output in receive bands) and the duplexer 115 may provide about 40 dB of isolation to suppress the transmitter band noise. Thus, self-interference noise power from the transmitter 105 is −160 dBm/Hz, which is 7 dB above the noise floor of the receiver −167 dBm/Hz (−174 dBm/Hz, which is 50 Ohm noise density, plus 7 dB, which is the noise figure of a typical receiver)
It would be desirable to suppress the transmitter noise to the level, when the total combined noise of the receiver and the transmitter generated noise in receive band will not degrade the total noise figure (NF) by more than 1 dB. In the example of FIG. 1, It would be expected to see a combined noise at −166 dBm/Hz, which will limit the transmitter generated noise to:
                    -        166            ⁢                          ⁢      dBm      ⁢              /            ⁢      Hz        -          (                        -          167                ⁢                                  ⁢        dBm        ⁢                  /                ⁢        Hz            )        ⁢          =                    2.5        ⁢                                  ⁢                  e                      -            17                          ⁢        mW        ⁢                  /                ⁢        Hz            -              2        ⁢        e            -              17        ⁢                                  ⁢        mW        ⁢                  /                ⁢        Hz              ⁢                  =                  0.5        ⁢                                  ⁢                  e                      -            17                          ⁢        mW        ⁢                  /                ⁢        Hz            ⁢                          =                        -          173                ⁢                                  ⁢        dBm        ⁢                  /                ⁢                  Hz          .                    Thus, it would be desirable to reduce the noise generated by the transmitter 105 by −160 dBm/Hz−(−173 dBm/Hz)=13 dB.